<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>
<body>
    <input type="number"> <button>发送</button>
    <script>
        var btn = document.querySelector('button');
        var time = 3;
        btn.addEventListener('click',function () {
            btn.disabled=true;
            var timer = setInterval(
                function() {
                    if (time==0) {
                        clearInterval(timer);
                        btn.disabled = false;
                        btn.innerHTML='发送';
                        time = 3;
                    } else {
                        btn.innerHTML = '还剩下' + time + 's';
                        time--;
                    }
                },1000 );
            
        })
    </script>
</body>
</html>